The present invention generally relates to an apparatus and method for acquiring, analyzing and imaging of three dimensional retinal data.
More specifically the present invention relates to a non invasive apparatus and method for measuring retinal thickness, surface topography and other features relating to the structure of the retina together with digital imaging of the retina, and correlating said structure with the retinal image.
The main cause of blindness in the western world is diabetic retinopathy. One of the most important pathologies of diabetic retinopathy is macular edema. Over a lifetime, about 30% of the people with diabetes will develop macular edema.
Non-proliferative diabetic retinopathy with Clinically Significant Macular Edema (CSME) includes either (a) thickening of the retina at or within 500 microns of the center of the macula or (b) hard exudates at or within 500 microns of the center of the macula if associated with thickening of the adjacent retina (not residual hard exudates remaining after the disappearance of retinal thickening) or (c) a zone or zones of retinal thickening 1 disk area or larger, any part of which is within 1 disk diameter of the center of the macula. Patients with CSME should be considered for treatment.
Recently a Retinal Thickness Analyzer (RTA) apparatus has been developed (U.S. Pat. No. 4,883,061). The RTA apparatus allows for visual inspection and for quantitative measurements of the retinal thickness, the amount of nerve fiber layer on the retina, the topography of the retinal surface, particularly that of the optic nerve head, and other additional features of the retina.
U.S. Pat. No. 5,742,374 teaches a fundus camera for photographing the fundus of an eye. The apparatus is provided with a ring slit illumination for peripheral illumination of the fundus. European Patent Publication No. 412667 teaches a fundus examining device including an optical system for observing an anterior portion of the eye. The apparatus disclosed is U.S. Pat. No. 5,742,374 and European Patent Publication No. 412667 are disadvantageous since the apparatuses disclosed do not enable analysis of the retinal thickness.
WO9730627 discloses a three dimensional imaging scanning apparatus for determining the retinal thickness and structure of the eye using non-invasive analysis. Optical paths and cameras are included for imaging both the whole fundus and the retinal thickness. For purposes of measurement of a specific region of the retina, both fundus imaging and imaging of the retinal thickness are used. The fundus imaging is specifically employed to determine relative positional orientation on the retina when selecting and also when subsequently comparing specific regions of the retina. Although WO9730627 utilizes a fundus camera, relatively complicated optics required for a professional fundus camera are not used. The fundus illumination is not homogeneous since it is performed in one direction (through the upper or lower part of the pupil). Imaging acquisition is also limited since it is not symmetric relative to the fundus. Therefore, the fundus camera can be used only as an accessory for a retinal thickness analyzer apparatus. The apparatus according to WO9730627 is disadvantageous since it can not be used as a medical diagnostic fundus camera device.
Also recently, fundus cameras used (i.e. for imaging retinas) are being modified for digital operation which allows for computerized processing, displaying and storing retinal electronic images.
The treatment for macular edema is by laser photocoagulation. The decision if and in what exact location on the retina the treatment is required, is based on an assessment regarding the retinal thickening and the location of the thickened areas.
The assessment of retinal thickening according to one known method is by slit lamp biomicroscopy and/or stereo fundus photography. The performance of this method is often difficult, inaccurate, and of questionable reliability. The information gained by using fundus cameras to perform Fluorescein Angiography shows areas of leakage in the retina which are seemed to be, but not necessarily are, the areas of thickening which have to be treated.
It is therefore of utmost necessity for an apparatus which may correlate the visual information gained from the fundus images with the thickness information gained from the RTA.
The present invention relates to such an apparatus, which combines the properties of an RTA and a digital fundus camera, by integrating the optical systems of the two instruments into a single system, which allows for acquirement of retina image data simultaneously (or in close succession) with retina thickness data, allowing a complete correlation in the registration of the two sets of data.
The present invention relates to an apparatus for acquiring, analyzing and imaging retinal reflected data, comprising a combination of at least one digital fundus camera and a Retinal Thickness Analyzer, using common optical, electrical and mechanical components, wherein a common optical combiner unit is included in the components, allowing peripheral illumination and centered image acquisition of the eye fundus by a fundus-camera, together with a lateral slit-illumination for sensing the retinal thickness by an off-center slit-camera
Additionally to the optical combiner unit, the common components include at least one common component from the following; (a) a common objective lens; (b) a common reticulation element for providing a fixation target; (c) means for simultaneously focusing light beams of the RTA and of the fundus camera, going to and returning from the retina; (d) common processing and displaying means for displaying images of the retina structure, tailored from plurality of images acquired by the RTA and combined together according to images acquired by the fundus camera; (e) a common energy source; (f) common control panel and housing; (g) a common mechanical support for positioning the patient""s face.
According to one variation of the apparatus, the common optical combiner unit is a removable dichroic mirror allowing acquisition of a high resolution slit image simultaneously with an average resolution fundus image, and the removable dichroic mirror is shifted out of the optical path for acquisition of a high resolution fundus image.
According to other variation of the apparatus, the common optical combiner unit is comprised of; (a) a central mirror for reflecting peripheral illumination onto the pupil and having an aperture at its center for transmitting the light returning from the retina to the fundus camera; (b) a first small mirror having an optical path disposed laterally off the center of the central mirror, for reflecting slit light onto the retina; (c) a second small mirror having an optical path disposed laterally off the center of the central mirror, for reflecting slit light returning from the retina to the slit camera; the two small mirrors are placed on two opposite sides of the central mirror. Preferably, the two small mirrors are integral parts of the central mirror, however, according to various considerations, they may also be positioned as separate parts, in front of the central mirror, or in the back of the central mirror, wherein the central mirror has two apertures conforming respectively with the optical paths of the small mirrors.
According to a preferred embodiment, the apparatus of the present invention has a first fundus camera for eye-fundus live image, and a second fundus camera for eye-fundus high resolution still image. Preferably, it further comprises a flash illumination source for acquiring still images.
In addition, the preferred embodiment of the apparatus comprise means for projecting a fixation target onto the examined eye of a patient, wherein the projecting means use at least in part the same optical path as the fundus camera. The embodiment also has a common focusing means for the slit light camera, the fundus camera and the fixation target projecting means.
The apparatus also utilizes a common power supply, a computer and a controlling unit for operating the slit light camera, the fundus camera, and associate electro-optical elements.
Preferably, the data acquired by the RTA slit camera and the data acquired by the fundus camera are combined automatically by the computer of the apparatus using an appropriate algorithm.
Preferably, in order to provide an improved distinction between light reflections associated with different cameras, the apparatus uses light sources of different wavelengths, or different color-filters.
Definitions
In the context of the present invention and accompanying claims, the term xe2x80x9cdigital fundus cameraxe2x80x9d relates only to a digital fundus camera. The term xe2x80x9cfundus cameraxe2x80x9d relates to a digital fundus camera or a non-digital fundus camera.
The eye fundus analyzer apparatus according to the present invention has two basic modes of operation:
Mode A: Fundus Camera mode:
In this mode the apparatus operates as a normal digital fundus camera as follows:
A continuous wave light source (in the visible or infra red spectrum) illuminates the retina. This illumination is a light beam projected onto the retina through the pupil of the examined eye and it is shaped so as to go through a predefined area of the pupil (which can be doughnut shaped). Shaping the beam is achieved by a shaped mirror located at a position optically conjugate to the pupil. Preferably, the mirror is doughnut shaped (i.e. having a hole at its center). The operator is aligning the apparatus such that the shaped illumination beam is outlined exactly at the pupil of the examined eye. Various color filters may be inserted in the beam to provide different contrasts for different features of the imaged retina.
An electronic TV (monochrome or color) camera, images the retina. The objective lens of this camera is the same lens through which the illumination beam is projected onto the retina. The illumination beam returning light (that goes from the retina to the camera) is restricted to a certain area of the pupil which is separate from the area through which the illumination beam is projected into the eye. This is achieved by routing the light to the camera through an aperture which is placed at a position conjugate to the pupil. (The aperture can be in the same shaped mirror which deflects and shapes the illumination beam). The camera is focused on the retina by movements of one or more lenses in the optical path (the movements may be achieved in any way known in the art). The electronic signal from the camera is directed to a TV or computer monitor (which may be formed as part of the camera or separately). The image acquired by the camera is continuously displayed on this monitor. The live image can also be recorded and stored by different electronic image acquisition methods as known in the art.
In addition, one or more still images can be acquired by the same camera. According to an aspect of the present invention, a pulse of light (which differs from the illumination beam in spectral content and/or intensity) is injected into the illumination beam during the acquisition of the still image, for obtaining improved contrast and resolution effects in the still image.
According to another aspect of the invention, a special still camera (preferably a high resolution camera) is added as a part of the apparatus. It is used to acquire a still image taking the advantage of using live images for aligning the apparatus. For the acquisition of the still image, a pulsed light source such as a flash lamp is used, additionally to the live image illumination beam.
Mode B: Retinal Thickness Analyzer (RTA) mode:
In this mode the apparatus operates as a Retinal Thickness Analyzer as follows:
A narrow slit of light (preferably a laser light) is projected onto the retina through a decentred area of the pupil of the examined eye.
The narrow slit light which illuminates the retina differs from the fundus camera illumination beam in one or more of the following:
(a) Its spectral content is different than that of the fundus camera illumination beam.
(b) One or more fixation target patterns which are seen by the examined eye are added by either subtraction or addition of light from/to the beam.
(c) The area on the pupil through which the fundus camera illumination beam passes is other than that through which the slit light passes.
The slit light scattered back from the retina is viewed by an electronic camera (hereinafter called xe2x80x9cslit cameraxe2x80x9d). The scattered light is restricted to pass through an area de-centered on the pupil and opposite to the area through which the slit light enters the eye. This is achieved by an aperture located on the light path at a point conjugate to the pupil. This causes the slit camera to view the slit image on the retina at an angle relative to the angle of the incident slit light. This allows for a quantitative measurement of the retinal thickness cross-section topography for the specific retinal area selected, and for optical sectioning of the retina.
During one measurement, the slit light is scanned over a number of positions on the retina so that the resulting image represents a number of cross-sections of the retina covering a square area of, for example, 2xc3x972 mm. It is possible, for example, that nine adjacent squares are scanned to provide coverage of an area of about 6xc3x976 mm (20xe2x80x3xc3x9720xe2x80x3) around the fovea, disk, or any other interesting zone. Immediately after the acquisition of the slit image, a still fundus image is acquired. The relative location of the slit image (or images) on the still image is known, according to the known relative positions of the optical paths used. This allows for a correlation between the information gained from the analysis of the slit images and the image information of the retina.
Likewise, numerous of either contiguous or dispersed scanned areas of the retina, can be represented in correlation with an image of the retina to enable a clinical and scientific evaluation.